The visual pathways of cats, tree shrews and squirrels are being studied with particular emphasis upon the structural changes that can be produced by visual deprivation. The binocular competition, which has previously been demonstrated by comparing monocular with binocular suture effects and by comparing the effects that a monocular suture has upon the different parts of the visual pathways, will be studied in more detail at geniculate and cortical levels. Light and electron microscopical methods will beused to study the geniculate and cortical neuronal organization and to study the effects of visual deprivation upon this organization.